The present invention relates generally to the field of internal combustion engines, and more specifically to engines operated under homogenous charge compression ignition principles and piston arrangements therefor.
An internal combustion engine combusts a fuel and air mixture within one or more combustion cylinders, and converts the energy from the combustion process into mechanical output energy. It has been known for many years to use spark ignition and combustion ignition concepts in internal combustion engines. In spark ignition engines, a mixture of fuel and air is provided to a combustion cylinder and compressed. A spark plug initiates combustion through the creation of an open spark sufficient to ignite the air and fuel mixture in the cylinder. Both two and four stroke operating sequences are known.
In a direct injection combustion ignition engine, such as a diesel engine, it also is common to use both two and four stroke operating sequences. Turbochargers are often used to supply a charge of air to the combustion cylinders at higher pressure and density than existing ambient conditions. On an upward stroke of the cylinder, the air intake ports are closed and the air is highly compressed. At the desired level of compression, fuel is sprayed into the cylinder by a fuel injector. The fuel ignites immediately, as a result of the heat and pressure inside the cylinder. The pressure created by the combustion of the fuel drives the piston downward in the power stroke of the engine.
Engine emission standards have led to the investigation of engine operating and compression ignition alternatives. In one such alternative, referred to as homogenous charge compression ignition (HCCI), significant reductions in emissions have been experienced during initial testing. In an engine operating under HCCI concepts, the air and fuel are intimately mixed, typically at a high air/fuel ratio, before maximum compression in the combustion cylinder. As a result, each droplet of fuel is surrounded by a quantity of combustion air in excess of that required for combustion. As compression occurs, the air temperature increases, and ultimately combustion is initiated at numerous locations throughout the cylinder. Typically, combustion commences at lower temperatures than for direct charge ignition, leading to reduced NOx emissions.
The use of homogenous charge compression ignition concepts has apparent benefits in substantial reduction of NOx emissions. However, two aspects of combustion control, used regularly in more conventional engines, are not available in an HCCI engine. The timing of ignition in an HCCI engine can be controlled neither indirectly by controlling the start of fuel injection, as in a direct injection engine, nor directly by controlling spark initiation, as in a spark ignition engine. Further, the rate of heat release can not be controlled via control of fuel injection, as in a direct injection engine, nor by flame propagation, as in a spark ignition engine. As a result, ongoing efforts for improving the HCCI concept include ways to control the ignition event in an HCCI engine.
To overcome these problems, attempts have been made to control the compression ratio in the combustion cylinder using a secondary cylinder in communication with the combustion cylinder. By varying the position and movement of a secondary piston in the secondary cylinder, the compression ratio in the combustion cylinder can be controlled. However, fully open secondary cylinders occupy significant space on the bottom deck of the cylinder head, making the placement, arrangement and operation of the standard aspiration valves more difficult.
U.S. Pat. No. 4,516,537 entitled, xe2x80x9cA Variable Compression System For Internal Combustion Enginesxe2x80x9d discloses a spark ignition engine in which a secondary cylinder and piston are provided to vary the compression ratio and reduce knock at low speeds and/or heavy loads, while also increasing power and fuel efficiency at high speed and/or light loads.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the invention, an internal combustion engine is provided with a combustion cylinder having an end, and a primary piston reciprocally disposed within the combustion cylinder. A cylinder head including a bottom deck at the end of the combustion cylinder. The cylinder head includes a secondary cylinder. A secondary piston is reciprocally disposed within the secondary cylinder. An actuator is coupled with the secondary piston for controlling a position of the secondary piston dependent upon a position of the primary piston, and thereby controlling commencement of a combustion event in the combustion cylinder. A communication port defined in the cylinder head establishes fluid flow communication between the combustion cylinder and the secondary cylinder.
In another aspect of the invention, a work machine is provided with a frame and an internal combustion engine carried by the frame. The internal combustion engine includes a combustion cylinder having an end, and a primary piston reciprocally disposed within the combustion cylinder. A cylinder head including a bottom deck at the end of the combustion cylinder. The cylinder head includes a secondary cylinder. A secondary piston is reciprocally disposed within the secondary cylinder. An actuator is coupled with the secondary piston for controlling a position of the secondary piston dependent upon a position of the primary piston, and thereby controlling commencement of a combustion event in the combustion cylinder. A communication port defined in the cylinder head establishes fluid flow communication between the combustion cylinder and the secondary cylinder.
In a further aspect of the invention, a method for operating an internal combustion engine is provided with steps of reciprocating a primary piston within a combustion cylinder having an end; reciprocating a secondary piston within a secondary cylinder adjacent the end, the reciprocating step being carried out such that the secondary piston has a position within the secondary cylinder which is dependent upon a position of the primary piston within the combustion cylinder; providing a combustable fuel to the combustion cylinder; communicating fluid flow between the secondary cylinder and the combustion cylinder, the communicating fluid flow step being carried out through a communication port having an opening in the combustion chamber and an opening in the secondary chamber, each the openings being narrower than the cylinders; and controlling commencement of a combustion event in the combustion cylinder through control of the position of the secondary piston.